Dear Dale You raise excellent points about the desirability of finding an "Alternative to Charcoal". I feel that the problem is both very complex, AND very simple at the same time. The problem is very complex, when dealt with, as a whole, but very simple when broken down into the various facets of the issue that complicate it.
If we look at the "continuum" between wood as a fuel, and charcoal as a fuel, we see that at the "Wood End" and the "Charcoal End", there is a clear preference, need, or requirement for the respective fuels. In the center, there is a "gray area", where either fuel can be utilized, to greater or lesser advantage and disadvantage. The problem is somewhat further complicated by those who see charcoal as a "climate change tool" and superimpose climate change considerations on stoves, perhaps even to the degree of relegating the fundamental heating and cooking aspects of a stove to a secondary level of importance. Everything starts with the biomass fuel... wood, grasses, agricultural products or waste, etc. In the logic I am about to lay out, I state that there are fundamentally three kinds of stove: 1: A "Full Combustion Biomass stove", where all fuel is intended to be burned to completion 2: A "Partial Combustion Biomass Stove", where char or charcoal is a desired end product. (This charcoal can be subsequently used as fuel, or as biochar.) 3: A "Charcoal Combustion Stove." In the interests of simplicity, I ignore "Charcoal Retorts", because of their basic thermal inefficiency.... much of the pyrolysis gas energy is simply vented. However, a retort that made use of the pyrolysis gas heat could be termed a "Partial Combustion Biomass Stove.' A major advantage of this approach would be that it would clearly categorize stoves, and as a consequence, would allow for three different testing protocols.Each Testing protocol could be set up to best capture the performance parameters that were of most importance to each stove system. Crispin's Proposed Stove testing Protocols are perhaps best for "Full Combustion Biomass Stoves." Equivalently relevant protocols could be developed for "Partial Combustion" and "Charcoal stoves. I feel that the process should be "Customer Driven." If a Customer wants to burn charcoal as fuel, then that is his decision. Or, if he wants to produce charcoal, for resale, or for use as biochar, or for subsequent use as a fuel, then that also should be his decision. This is where a good set of Testing Protocols would be really helpful... they would allow the Customer to select the stove system (or systems) that best met his needs. Note also that when fundamental "performance information" was available from the above three protocols, it would be very easy to develop a spread sheet that factored in all the relevant information, so that the Customer could make a rational decision on what would be the best stove system for his particular circumstances. Best wishes, Kevin . ----- Original Message ----- From: Andreatta, Dale A. To: Discussion of biomass cooking stoves Sent: Monday, April 08, 2013 6:09 PM Subject: [Stoves] Alternative to charcoal At the recent ETHOS conference Paul Means and Chris Lanning gave a very thought-provoking talk about an alternative to charcoal. The basic idea was to use a gasifying stove with prepared wood fuel. The prepared wood fuel would be bought by the user instead of charcoal, and the supply chain would be similar to charcoal. The big advantage is that the very inefficient step of charcoal production is eliminated. The stove would hopefully be easy to use and would smoke very little, so as to retain the benefits of a charcoal stove. Their proposed fuel was crumbled wood, which would work well, but seemed to me to require a lot of big machinery and capital. How could one go from a tree to a fuel that would burn well in a gasifier with as little work as possible, and without too much costly equipment? The fuel should be as low or lower in cost than charcoal per unit of food cooked, and give a better ratio of food cooked per unit of tree. I did some preliminary experiments. With 779 g of natural wood from the trees in my yard, I used a Paul Anderson Champion gasifier and boiled 5 liters in 21.4 minutes (corrected). After an easy light the stove burned steadily with no attention, other than turning down the primary air when boiling started. About 10 minutes after boiling the pyrolysis ended and I transferred 123 grams of char sticks, glowing only weakly, into a charcoal stove, and continued simmering until nearly 2 hours after the start of boiling. I had good turndown on the charcoal stove and a lid on the pot. There was a little smoke during the pyrolysis phase, but not too much. This seems like excellent stove performance. Had I used a very good charcoal stove to perform a similar task, it might have taken 240 g of charcoal. This would take about 1800 g of wood if the charcoal were made efficiently, or 3000 g if it were made normally. (Reference Means and Lanning on the efficiency of charcoal production.) The wood I started with was about 1 inch diameter (2.5 cm) by 6 inches (15 cm) long, cut from my trees and dried outdoors but under cover for some months. I didn't measure the moisture content, but a previous oven-drying test with similar wood showed about 12-14% moisture. A previous test with larger diameter wood didn't go well, so I think this is about the maximum possible diameter. I don't know how long it took to get to this moisture content, not months I'm sure, but at least some number of days. The production method for this alternative to charcoal would be to use a chain saw to cut wood into convenient lengths while in the forest, then take it to a central place. Here, use electric saws and/or hydraulic splitters to cut the wood to the appropriate size. Give the wood a modest amount of drying in the sun, or in some simple oven. The wood might have to finish drying at the place of use. I expect that split wood would dry faster than cut sticks, since the moisture doesn't have to pass through the bark. Alternatively, use a chain saw and engine powered splitter to cut the wood to size in the forest, then transport to a central place for drying. When fairly dry, transport the wood to the users as with charcoal. During transport, the energy per unit weight would be lower than charcoal, but the energy per unit volume would be similar. The user might be given the option of buying shorter sticks for cooking smaller meals, or longer sticks for larger meals. In comparing the economics of this method to charcoal, I would think of the cost of the fuel as coming from 5 elements; the cost of the trees, the cost of the processing equipment, the cost of the labor, the cost of the transportation and distribution, and the cost of the stove. If the trees are free, then the fact that you don't cut as many trees doesn't help much. If the trees must be paid for, then this method looks more attractive. The processing equipment for charcoal is virtually free, but hopefully this method doesn't take too much equipment. The labor for this method might be similar to charcoal, but it might be less because you are cutting and processing a lot fewer trees to serve the same number of customers. Transportation would be more expensive, since you are shipping more mass, though not a lot more volume. This method would require a gasifier or T-Char stove, which would be an expense, though hopefully not a lot compared to the annual cost of fuel. Thus, if the trees must be paid for, this method might be attractive to the consumer of the fuel, the producer of the fuel, and to the forest. If the trees are not paid for, this method looks less attractive, though the forest would still benefit and some outside subsidy might be available. Dale Andreatta, Ph.D., P.E. ------------------------------------------------------------------------------ _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org for more Biomass Cooking Stoves, News and Information see our web site: http://stoves.bioenergylists.org/
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